Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Update all script shebangs to use /usr/bin/env interpreter instead of /bin/interpreter
This is required to support systems where bash doesn't reside in /bin (such as NixOS, or the *BSD family) and allow users to specify a different interpreter version through $PATH manipulation.
https://www.cyberciti.biz/tips/finding-bash-perl-python-portably-using-env.html
```release-note
Use /usr/bin/env in all script shebangs to increase portability.
```
Don't revert, change boundingdirs in Makefile for deepcopy-gen
manually fix pkg/client/clientset_generated/clientset/typed/core/v1/pod_expansion.go because external policy types are moved now
Lots of places used sort (or sort -u) but didn't set LC_ALL=C. This
means it could be slightly different on different people's systems. Make
it deterministic.
This operation takes 2-5 seconds on every build, but doesn't actually need to
run most of the time. Now we cache it and see if it needs a rebuild (fast)
before actually rebuilding (slow).
Tim Hockin